For example, in a retractor (including a rewinding function) for a long object such as a strip or a string, a winding drum (also called a drum or a spool) that retracts a long object rotates relative to a support unit that rotatably supports the winding drum. It is preferable to dispose an energy absorbing device between relatively moving objects since a large load is applied to the apparatus and the long object when the long object is fully extended or when the winding drum stops during retracting or rewinding of the long object in the apparatus which performs a relative movement. Typically, an example of such a retractor is a seat belt retractor used in a seat belt apparatus (for example, see Patent Literature 1 or 2).
Patent Literature 1 discloses a seat belt retractor in which a torsion bar and a wire are disposed between a winding drum and a ratchet gear which relatively rotate. This seat belt retractor can absorb an energy generated between the winding drum and the ratchet gear due to twisting deformation of the torsion bar and sliding deformation of the wire, and can change the energy absorbing properties by varying a withdrawing load necessary for sliding deformation of the wire.
Patent Literature 2 discloses a vehicular force limiter in which ring discs (1, 3) and an oscillation member (2) are disposed between relatively rotating objects. In the above limiter, when the oscillation member (2) rotates relative to the ring discs (1, 3), projections (5) formed on the oscillation member (2) come into contact with projections (7, 8) formed on the ring discs (1, 3) while oscillating alternately, thereby absorbing an energy generated between the relatively rotating objects. In particular, in the above limiter, a kinetic energy varies depending on a rotation speed of the oscillation member (2), and an energy absorbing amount can be increased with increase of the rotation speed of the oscillation member (2).